The earliest clearly British Christian leader recorded after the departure of the Roman legions from the island was Saint Dyfrig (Latin, Dubricius). He is said to have been a son of Eurddyl and her husband King Pabai or Pepiau of Ercych (now Herefordshire). He founded monasteries at Henllan ("Old Church"), now Hentland-on-Wye, 7 kilometers northwest of Ross-on-Wye; at Mochros, now Moccas, in the Wye Valley 16 kilometers west of Hereford; at Ynys Pyr (English, "Caldey Island"), off Tenby in the Dyfed county of Pembrokeshire; and possibly churches in Porlock and near Luscombe on the Exmoor coast of Somerset. Armorica's southern boundary extended to the Pyrénées. He was a bishop, but it appears that he was so for the purpose of ordaining priests, not as administrative head of the church over a geographical area. There is a legend that he solemnised the marriage of King Arthur and Guinevere.

Pol, son of a British chieftain and one of the seven founder saints of Brittany, founded churches near Llandovery in the Dyfed county of Carmarthenshire, and before 518 had founded an abbey at Yr Henllwyn ("Old Bush") called Ty Gwyn ("White Church"). He later founded monasteries in Brittany and was first bishop of the city of Saint-Pol-de-Leon. His sister was St. Sidwell of Exeter. Samson was born in Dyfed. He was a first cousin of Illtud and a great-grandson of King Tewdrig (Tudor) of Morganwg (Glamorgan). He studied as a boy at Llan Illtyd Fawr and was then sent to Ynys Pyr, presently becoming its abbot. Some time after 545 he temporarily took over the abbacy of Llan Illtud Fawr from Illtud. When Illtud resumed charge of his abbey, Samson travelled first to Cornwall and then to Brittany, founding churches in both places and an abbey at Dol, where he died c.565. He is also celebrated as the evangeliser of Guernsey.

The Druids after long supporting their power and influence, were obliged to fly from the ferocious sword of the Romans to Anglesea. Followed thither by the universal conquerors, they made a noble stand; but being defeated, their king, Caractacus, was carried in chains to Rome, and the whole race nearly exterminated.In the early days — say from the tenth century on to probably the fourteenth or fifteenth centuries, the Parish of Michael, or "Kirk Michael" as it was then called, must have been a very important place for two main reasons, the first being that in those early days sittings of Tynwald were regularly held there, and, secondly, that the official residence of the Lord Bishop was in the parish.

St. Cadoc came into conflicts with kings Arthur, Maelgwn of Gwynedd, and Rhain of Brycheiniog. Beneventum, east of Daventry in Northamptonshire. was overrun by Saxons at this time as an explanation both for both the killing of Cadoc and for the prohibition on Britons entering the town to recover his body. Cadoc, with Illtud, is one of the three knights said to have become keepers of the Holy Grail. A brother of this King Gwynllyw was Saint Petroc.

Petroc in Ireland perhaps learned esoteric Druid wisdom as well as Christianity. He spent most of his adult life based at Padstow in Cornwall, and founded churches in Cornwall, Devon and Somerset (all then part of Dumnonia / Kernyw) including North and South Petherton (places named after him in west and south Somerset respectively). He converted King Constantine of Dumnonia (in 586) and died in 590. With Saint Piran he is among the best-known of the Cornish saints. The principal contemporary leader of the church in the north of Romanised Britain was Saint Kentigern / Mungo, a son of King Urien Rheged (ruled c. 560 to c. 590), the founder of Glasgow Cathedral and its first bishop.

Germanus, for the honour of the Manks nation, was sixty-nine years ancienter than Bangor, in Wales, which was the first bishopric that we read of among the Britons, and one hundred and fourteen years before Austin the monk. He introduced the liturgy of the Lateran, and so absolutely settled the business of religion, that the Island never afterwards relapsed. He died before St. Patrick, who sent two bishops to supply his place, Conindrius and Romulus, of whom we have little memorable; but that one or both of them survived St. Patrick five years is very probable, for then it was 494. The Latin Church was brought to Canterbury by St. Augustine and his forty Benedictine Monks in 597 A.D.

The ancient British Traids list Joseph and his company as Culdees along with Paul, Peter, Lazarus, Simon Zelotes, and Aristobulus and before the Synod of Whitby the Celtic Catholic church was known as Culdee Christian Church and there is evidence that this name lived on past the Synod of Whitby until at least the reign of Henry II where the Canons of York where known the "Culdee Canons".

In Cornwall, the same group in Brittany had been led by St. Breaca, a nun of Kildare (Thomond) and included Ronan who is represented as a son of two converts of Saint Patrick. Saint Ronan returned to Ireland but was soon back in Cornwall to Brittany in about 500. The beginning of the church organization was with no episcopal jurisdiction as it ws practiced in Gaul. The numerous clerics in episcopal orders among the migrants assumed no administrative duties in Brittany. Thus the church of the Britons in Brittany was a new creation, reflective of the pattern of the mother church in Cornwall and Wales. Many of parishes arose in previously unpopulated or unchristianized areas where no parish organization had preceded. The coming of saints with dozens of companions is an arrangement with many Irish parallels. Such groups in Brittany are of six-century date and no membership in missionary action.

St. Budoc from the fifth century was the child of parents who had already settled Brittany. Born in a sealed cask in which his mother had been put to sea, released with her at Waterford where he grew, the crosses the sea to Brest, floating on a stone coffin. It is possible that he restored the ruins of a church built in Roman times on the tiny island of Lavret off Plaimpol, and founded a monastery there. St Budoc is associated with St. Mawes who settled on the island of Modez off the Leon coast. St. Brieuc of Cardiganshire descended from Maximus Magnus and was known in Wales as Tyfriog and dates elude to St. Tudwal, said to have been Brieu'c nephew and the cousin of a ruler of Damnonia in the north central Brittany. The Tudwal foundation was called Lan Pabu.

St. Samson of Dol, the Welsh saint was probably over sixty when he reached Brittany. He had epsicopal orders while in Wales and in the ninth century his monastery of Dol gave rise to an episcopal see, referred to as the Bishop of Dol. The 610 AD anonymous writing of Life of Samson makes no other statement than Samson as abbot. The later abbot of Dol, Tigernomalus was also of episcopal rank with a troupe of fellow clerics Samson landed at the mouth of the Gouioult which flows into the Bay of St. Michel, and moving to higher ground, instituted the monastery of Dol. Many monasteries of the province of Devon extended through a great area of northeastern Brittany. When Judwal was imprisoned by King Childebert at Paris, the signatory Samson took upon himself of effecting Judwal's release and successfully attended the Third Council of Paris and founded the monastery at Pentale on the Seine. He set out on a mission in the Channel Islands of Jersey and Guernsey, extending to some of the Scilly Isles, where his name is also remembered but he ended his days at Dol.

The Christianization of Ireland took place within the period of the movement with the rise of monasticism and its spread from Egypt, Palestine, and Asia Minor to all parts of western Europe. In Gaul the first monastic personality was Saint Martin (325-397), a native Pannonia (Hungary) who left the Roman army, founded a monastery at liguge in 360, became bishop of Tours. Anthony in Egypt, Martin of Gaul, Illtud and David in Britain and Ninians successors at Candida Casa- the institution was called Rosnat by the Irish, referred to as the Great Monastery. The monastic contact of Ireland with Wales in the era of the great Welsh saints gives prominence to Gildas. Samson of Dol accompanied some Irish from Wales to Ireland. Cadoc's treacher in Wales is the son of an Irish king, St. Carranog (Cernach) in Irish documents joined Patrick in Leinster. Before St. Finian found a monastery of Clonard, he was brought by Cadoc to Wales. After his adoption of monastic life, Columba went for instruction to the bard Gemman and resided for a time in Leinster.

Enda's settlement was accompanied across Galwy Bay by a band of disciples to Monastirboice in County Louth. After 500, Ciaran, the founder of Clonmacnois in Offaly is a reputed disciple of St. Enda and thus an heir of the Whithorn school of learning. Clonmacnois maintained a front-rank position in Irish monasticism to the age of the Vikings where Finian, abbot of Clonard in meath established the monastery about 520 with association of Welsh saints. Among the twelve apostles of Ireland: Columba of Iona, St. Ciaran of Clonmacnois, St. Brendan of Birr, St. Brendan of Clonfert the Voyager. Brendan the Voyager came from County Kerry and it was in the Dingle peninsula that a number of small communities and neighboring islands led to the foundation on Inishglora off the coast of Mayo and a nunnery at Annaghdown on Lough Corrib in Galway, he placed under his sister Brig. As a friend of Columba, formed a community on Tiree and at some time reached Iceland. On the Dingle peninsual in Kerry, Dunmore Head is the westermost point of ireland and the next parish to America. On the lofty island rock of Scellig Michael, eight miles out in the ocean from the coast of Kerry, countless seaside setllements on Ireland's coasts and among the Hebrides, the next generation came Columba, like Enda and Finian of Moville, was an Irish Pict.

St. Kevin (Coemgen), a descendant of kings of Leinster was sent as a boy to study at Kilnamanagh near Tallach, County Dublin. Here he was instructed by St. Petrock, a Cornwall monk and scholar. Kevin settled in the solitude of Glendalough (Valley of the Lakes) in County Wicklow and cultivated boats and fishing among the two lakes. Among the Wicklow Mountains, tribes of Dublin and Kerry, Meath, Nass, Ossory and Leix had settled as well as the monastic settlement of the Franciscans, the Úí Cheinnselaig expanded into Wexford down the Slaney valley through a pass between the Balckstairs and the Wicklow Mountains, and the Ulaid residence of Crew Hill. Newcastle was an English Bourough by-name brought from Domesday and the Treaty of Montgomery. A place in Munster of the Uí Faelain; and O'Brien branch of the Wicklow mountains who unlike the Ua Faelain of the Déisi who had anglicanized lordships. Naas Chiefs of Hy-Maile [Imaile] and of Hy-Teigh or Maine Mál comprised Cualan's Country or the mountain land baronies.

St. Patrick was proceeding south-wards on his mission of love along the eastern shore of Lough Neagh (Loch nEathach), and at his word the fierce inhabitants of Dalaradia were yielding to the gentle influence of the Gospel. By the eighth century, then, the main northern branches of the Érainn and Cruthin were confined east of the lower Bann and the Newry river.